1. Field of the Invention
The present invention relates to a method of removing heavy metals from factory effluents, industrial garbage, sludge, and marine organisms, all of which contain heavy metals, as well as to a system for use with this method and to a method of precipitating protein at the time of removal of heavy metals.
2. Description of the Related Art
Effluents or garbage from factories are generated in the fields of mining, chemical engineering, and metals. To prevent environmental pollution, industrial wastes are processed after heavy metals have been removed from them, and the water used for removing heavy metals from the wastes is released after it has been purified to such a level as to satisfy environmental standards for discharge.
In accordance with conventional methods of removing heavy metals from heavy-metal-containing materials, sodium hydroxide is added to react with heavy metals such as Cr or Zn to thereby form Cr(OH).sub.2 or Zn(OH).sub.2. The heavy metals are then precipitated by addition of a macro molecular coagulant to the thus-formed hydroxides, and supernatant liquid resulting from precipitation is released.
From the viewpoint of environmental protection, the standards for discharging water used for removal of heavy metals have recently been rendered more rigorous, and satisfying the discharge standards through use of the conventional method has become difficult. Specifically, heavy metals must be removed from the water to a much greater extent.
In recent years, it has been acknowledged that innards of fish or shellfish contain a large quantity of heavy metals, and therefore the innards cannot be disposed of without removal of heavy metals.